link scheduling queuing
Download
Skip this Video
Download Presentation
Link Scheduling & Queuing

Loading in 2 Seconds...

play fullscreen
1 / 20

Link Scheduling & Queuing - PowerPoint PPT Presentation


  • 115 Views
  • Uploaded on

Link Scheduling & Queuing. COS 461: Computer Networks http://www.cs.princeton.edu/courses/archive/spr14/cos461/. Outline. Link scheduling (not covered on Monday) Queuing practice questions Miscellanea. First-In First-Out Scheduling. First-in first-out scheduling Simple, but restrictive

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Link Scheduling & Queuing' - cairo-hicks


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
link scheduling queuing

Link Scheduling & Queuing

COS 461: Computer Networks

http://www.cs.princeton.edu/courses/archive/spr14/cos461/

outline
Outline
  • Link scheduling (not covered on Monday)
  • Queuing practice questions
  • Miscellanea
first in first out scheduling
First-In First-Out Scheduling
  • First-in first-out scheduling
    • Simple, but restrictive
  • Example: two kinds of traffic
    • Voice over IP needs low delay
    • E-mail is not that sensitive about delay
  • Voice traffic waits behind e-mail

3

strict priority
Strict Priority
  • Multiple levels of priority
    • Always transmit high-priority traffic when present
  • Isolation for the high-priority traffic
    • Almost like it has a dedicated link
      • Except for (small) delay for transmission
  • Possible starvation

High

Low

4

weighted fair queuing
Weighted Fair Queuing
  • Each queue gets a fraction of the link bandwidth
  • Rotate across queues on a small time scale
  • What if a queue is empty during its time slice?
    • Move on to next queue if work conserving

50% red, 25% blue, 25% green

5

weighted fair queuing1
Weighted Fair Queuing
  • If non-work conserving
    • Flows get at most their allocated weight
  • If work-conserving
    • Send extra traffic from one queue if others are idle
    • Bytes, not packets
    • Higher or lower utilization than non-work conserving?
  • Results in max-min fairness
    • Maximize the minimum rate of each flow

6

implementation trade offs
Implementation Trade-Offs
  • FIFO
    • One queue, trivial scheduler
  • Strict priority
    • One queue per priority level, simple scheduler
  • Weighted fair scheduling
    • One queue per class, and more complex scheduler

7

slide8

For the following questions, assume that these are always coupled with a FIFO scheduling policy.

The full queue problem occurs if routers’ queues are often full.

The lockout problem refers to a situation where a small number of flows monopolize the available queue space on a router.

  • Drop-tail solves the full queue problem T/F
slide9

For the following questions, assume that these are always coupled with a FIFO scheduling policy.

The full queue problem occurs if routers’ queues are often full.

The lockout problem refers to a situation where a small number of flows monopolize the available queue space on a router.

  • Drop-tail solves the full queue problem T/F
slide10

For the following questions, assume that these are always coupled with a FIFO scheduling policy.

The full queue problem occurs if routers’ queues are often full.

The lockout problem refers to a situation where a small number of flows monopolize the available queue space on a router.

  • Drop-tail solves the full queue problem T/F
  • Random Early Detection (RED) solves the full queue problem T/F
slide11

For the following questions, assume that these are always coupled with a FIFO scheduling policy.

The full queue problem occurs if routers’ queues are often full.

The lockout problem refers to a situation where a small number of flows monopolize the available queue space on a router.

  • Drop-tail solves the full queue problem T/F
  • Random Early Detection (RED) solves the full queue problem T/F
slide12

For the following questions, assume that these are always coupled with a FIFO scheduling policy.

The full queue problem occurs if routers’ queues are often full.

The lockout problem refers to a situation where a small number of flows monopolize the available queue space on a router.

  • Drop-tail solves the full queue problem T/F
  • Random Early Detection (RED) solves the full queue problem T/F
  • RED solves the lockout problem for TCP flows T/F
slide13

For the following questions, assume that these are always coupled with a FIFO scheduling policy.

The full queue problem occurs if routers’ queues are often full.

The lockout problem refers to a situation where a small number of flows monopolize the available queue space on a router.

  • Drop-tail solves the full queue problem T/F
  • Random Early Detection (RED) solves the full queue problem T/F
  • RED solves the lockout problem for TCP flows T/F
slide16

1 Drop-tail has fewer burst losses than RED

T/F

2 Both drop-tail and RED can be used with Explicit Congestion Notification (ECN), so the router can signal congestion to the sender without dropping a packet

T/F

slide17

1 Drop-tail has fewer burst losses than RED

T/F

2 Both drop-tail and RED can be used with Explicit Congestion Notification (ECN), so the router can signal congestion to the sender without dropping a packet

T/F

slide18

1 Drop-tail has fewer burst losses than RED

T/F

2 Both drop-tail and RED can be used with Explicit Congestion Notification (ECN), so the router can signal congestion to the sender without dropping a packet

T/F

3 RED drops every incoming packet with some probability P > 0

T/F

slide19

1 Drop-tail has fewer burst losses than RED

T/F

2 Both drop-tail and RED can be used with Explicit Congestion Notification (ECN), so the router can signal congestion to the sender without dropping a packet

T/F

3 RED drops every incoming packet with some probability P > 0

T/F

tcp windows
TCP Windows
  • Receive window
    • flow control
  • Congestion window
    • Additive increase / multiplicative decrease
    • Triple duplicate ACKs
    • Slow-start, fast retransmit, fast recovery, etc.
ad